Method for obtaining a surface of titanium-based metal implant to be inserted into bone tissue

ABSTRACT

The invention relates to a method for obtaining a surface of a titanium-based metal implant intended to be inserted into bone tissue, comprising: (a) projecting particles of aluminium oxide under pressure on the external area of the implant; (b) chemically treating the sandblasted external area of the implant with an acid composition comprising sulfuric acid and hydrofluoric acid; and (c) thermally treating the sandblasted external area of the implant by heating at a temperature of 200-450° C. for 15-120 min. The invention likewise defines a metal implant having said surface. The surface thus obtained has good micrometer-scale roughness with a suitable morphology, as well as a composition which is virtually free of impurities and a thickness which is approximately three times the thickness of conventional surfaces, which characteristics provide it with very good osseointegration properties.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a division of 12/720,664 filed on Mar. 9,2010, which is a continuation under 35 U.S.C. 120 of InternationalApplication PCT/ES2007/000555 filed Oct. 3, 2007, which claims priorityto Spanish Patent Application No. P200702414 filed Sep. 10, 2007, thecontents of each of which are incorporated herein by reference.

FIELD OF THE INVENTION

The invention relates to the field of metal implants to be inserted intobone tissue. Specifically, the invention refers to a method forobtaining a metal implant surface that exhibits good roughness and hasan optimised chemical composition and thickness resulting in a bettercellular response, and therefore, a better implant-bone binding. Theinvention also refers to the metal implant that exhibits it.

BACKGROUND OF THE INVENTION

As is well known in the state of the art, some metals or metal alloys,such as titanium, zirconium, hafnium, tantalum, niobium, or alloysthereof, are used to form relatively strong links with bone tissue. Inparticular, metal implants of titanium and its alloys have been knownsince approximately 1950 for their properties of binding well to bonetissue. This binding was called osseointegration by Branemark et al.(Branemark et al., “Osseointegrated implants in the treatment of theedentulous jaw. Experience from a 10-year period”, Scand. J. Plast.Reconstr. Surg., II, suppl 16 (1977)).

Although the binding between this metal and bone tissue is relativelystrong, it is desirable to improve this binding. There are many methodsdeveloped in the state of the art to treat such metal implants to obtaina suitable surface on them to improve their osseointegration. The term“surface” is understood to refer to the superficial layer or mostexternal zone of an implant, composed mainly of the oxide of thecorresponding metal, the physical properties of which are clearlydifferent from the massive material that the implant is made of.

Some of these methods are directed to altering the morphology of thissuperficial layer, increasing its roughness, in order to provide ahigher area of contact, and therefore of binding, between the implantand the bone tissue, resulting in higher mechanical retention andstrength, that is, in a better osseointegration of the implant.

The reason behind these procedures for increasing surface roughness arethe studies carried out in the last few years (Buser et al., “Influenceof surface characteristics on bone integration of titanium implants. Ahistomorphometric study in miniature pigs”, J Biom Mater Res, (1991),25:889-902; Wennerberg et al., “Torque and histomorphometric evaluationof c.p. titanium screws blasted with 25- and 75-um-sized particles ofAl₂O₃ ”, J Biom Mater Res, (1996); 30:251-260; Buser et al., “Removaltorque value of titanium implants in the maxilla of miniature pigs”, JOral Maxillofac Implants (1998) 13:611-619; and Lazzara et al., “Boneresponse to dual acid-etched and machined titanium implant surfaces”,Bone Engineering, chap. 34 (2000) J. E. Davies eds.), which demonstratethat osseointegration of the implant in the short and medium term isimproved by a micrometric surface roughness.

Also, other studies (Buser et al. 1991, supra; Cochran et al.,“Attachment and growth of periodontal cells on smooth and roughtitanium”, Int. J. Oral Maxillofac Implants (1994) 9:289-297; Martin etal., “Effect of titanium surface roughness on proliferation,differentiation, and protein synthesis of human osteoblast-like cells(MG63)”, J Biom Mat Res (1995) 29:389-401; Lazzara et al. 2000, supra;and Orsini et al., “Surface analysis of machined vs sandblasted andacid-etched titanium implants”, J. Oral Maxillofac Implants (2000)15:779-784) have demonstrated that the existence of a superficial layeron the implant of a micrometric roughness improves osteoblast cellularexpression, giving rise to better cellular differentiation and betterosteoblast expression. The consequence of this effect is an improvedosseointegration and a more bone formation.

Also, some more research-based manufacturers, such as Nobel Biocare,have designed such surface treatments so that they increase thethickness and the crystallinity of the titanium oxide layer, as somestudies seem to suggest a relationship between the degree ofcrystallinity and better osseointegration of the implant (Sul et al.,“Oxidized implants and their influence on the bone response”, J MaterSci: Mater in Medicine (2002); 12:1025-1031).

The methods used in the state of the art to increase surface roughnessof an implant are very diverse. Among them can be highlighted theapplication of a coating over the surface, blasting of the surface withparticles and chemical attack of the surface.

The common methods of coating the metal implant surface consist inapplying a metal coating, normally of titanium, or a ceramic layer,normally of hydroxyapatite, by various known techniques such as plasmapulverisation or plasma spray (Palka, V. et al., “The effect ofbiological environment on the surface of titanium and plasma-sprayedlayer of hydroxylapatite”. Journal of Materials Science: Materials inMedicine (1998) 9, 369-373).

In the case of blasting the surface, particles of various materials andsizes are used, which are blasted on the surface of the implant in suchas way as to alter its morphology. Usually, particles of corundum(alumina) are used (Buser et al. 1991, supra; Wennerberg et al. 1996;supra), or particles of titanium oxide (Gotfredsen, K. et al.,“Anchorage of TiO2-blasted, HA-coated, and machined implants: anexperimental study with rabbits”., J Biomed Mater Res (1995) 29,1223-1231).

On the other hand, chemical attack of the surface is carried out usingvarious mineral acids such as hydrofluoric acid, hydrochloric acid,sulfuric acid, etc. So, for example, in a series of United Statespatents by Implant Innovations Inc. (U.S. Pat. No. 5,603,338; U.S. Pat.No. 5,876,453; U.S. Pat. No. 5,863,201 and U.S. Pat. No. 6,652,765) atwo-stage acid treatment is described that is used to obtain thecommercial Osseotite® surface. In the first stage, aqueous hydrofluoricacid is used to remove the natural oxide layer on the metal surface; inthe second stage a mixture of hydrochloric acid and sulfuric acid isused to obtain a micrometric rough surface. In the European patentapplication EP 1477 141, also from Implant Innovations Inc., a variationof this method is described in which a mixture of hydrofluoric acid andhydrochloric acid is used in the second stage to treat implant surfacesbased on titanium and Ti6Al4V alloys.

The combined use of both techniques has also been described, that is,blasting of the implant surface followed by chemical attack. So, Buser(Buser et al. 1991, Buser at al. 1998, supra) described, among othermethods, blasting with medium grain alumina followed by etching with amixture of hydrofluoric and nitric acids; also blasting with coarsealumina followed by chemical treatment with a mixture of hydrochloricand sulfuric acids. Similarly, Cochran (Cochran et al. 1994, supra) usedblasting with fine or coarse corundum particles followed by a chemicaltreatment with hydrochloric and sulfuric acids to treat a titaniumsurface. Similarly, Choi Seok et al. (KR 2003007840) described blastingwith calcium phosphate particles followed by treatment with a mixture ofhydrochloric and sulfuric acids. Equally, in the document WO 2004/008983by Astra Tech, a method of treatment of implant surfaces was describedthat combined blasting with fine and coarse particles of titanium oxidefollowed by treatment with hydrofluoric acid. Also, Franchi (Franchi etal., (2004) “Early detachment of titanium particles from variousdifferent surfaces of endosseous dental implants”, Biomaterials 25,2239-2246) and Guizzardi (Guizzardi et al., (2004) “Different titaniumsurface treatment influences human mandibular osteoblast response”, JPeriodontol 75, 273-282) described blasting with fine and coarsezirconia particles followed by an unspecified acid treatment.

Regarding thermal treatment, Browne (Browne et al. (1996),“Characterization of titanium alloy implant surfaces with improveddissolution resistance”, Journal of Materials Science: Materials inMedicine 7, 323-329) and Lee (Lee et al. (1998), “Surfacecharacteristics of Ti6Al4V alloy: effect of materials, passivation andautoclaving”, Journal of Materials Science Materials in Medicine 9,439-448) described the treatment of a previously untreated titaniumalloy with hot air at 400° C. for 45 minutes to achieve betterresistance to dissolution and a higher thickness of the oxide layer;although the thickness achieved was only 4 nm.

By means of these methods, therefore, surfaces with micrometricroughness are obtained but with a very much reduced surface titaniumoxide thickness, which entail the disadvantages of not having a verystable titanium oxide layer and not reducing the release of metal ionsto the medium.

The state of the art, therefore, continues to require alternativemethods of treating the superficial layer of metal implants that providea micrometric surface roughness and with improved chemical compositionand thickness in order to optimise the process of theirosseointegration.

Spanish patent application 200701518 of the present authors describes amethod for obtaining a surface of titanium-based metal implants which isvirtually free from impurities, with a thickness which is approximatelythree times the thickness of conventional surfaces, and with amicrometer-scale roughness and morphology (FIGS. 1 a and 2 a) optimizingthe osseointegration and bone anchorage processes.

Said method consists of projecting particles of zirconium oxide underpressure to sandblast the external area of the implants, followed by asubsequent chemical treatment with a particular combination of acids andby a final thermal treatment. The use of a mixture of sulfuric acid andhydrofluoric acid, as well as the combination of these three treatmentand the conditions of the final thermal treatment had not been describeduntil then.

The present inventors have now found that in the sandblasting process ofthe previous method, the substitution of the type of particles togetherwith the modification of their size and the pressure at which they areprojected allows obtaining an alternative surface of a metal implantwith a micrometer-scale morphology which is different but also suitablefor optimizing the osseointegration and bone anchorage processes.

Therefore, the method of the present invention allows obtainingalternative surfaces of titanium-based metal implants with optimizedproperties in relation to chemical composition, thickness, andmicrometer-scale roughness and morphology which translate into goodosseointegration and cell response properties.

OBJECT OF THE INVENTION

The object of the present invention is, therefore, to provide a methodfor obtaining a surface of a titanium-based metal implant intended to beinserted into bone tissue.

Another object of the invention is to provide the surface obtainable bysaid method.

Finally, another object of the invention is to provide a metal implantthat exhibits said surface.

DESCRIPTION OF THE DRAWINGS

FIG. 1 a shows a micrograph (150×) of the surface obtained by theprevious method of the present inventors.

FIG. 1 b shows a micrograph (150×) of the surface obtained by the methodof the invention.

FIG. 2 a shows the roughness in three dimensions obtained by confocalmicroscopy of the surface obtained by the previous method of the presentinventors.

FIG. 2 b shows the roughness in three dimensions obtained by confocalmicroscopy of the surface obtained by the method of the invention.

FIG. 3 shows the reconstruction of the sector of an outer thread area ofthe implant and the measurement of the corresponding roughness of thesurface obtained by the method of the invention.

FIG. 4 shows the energy-dispersive X-ray spectrum (EDS) of the surfaceobtained by the method of the invention.

FIG. 5 shows the cell viability at 12, 24 and 72 hours as an indicatorof the cytotoxicity of the surface obtained by the method of theinvention (03/136/14) with respect to that of other conventionalsurfaces.

FIG. 6 shows the alkaline phosphatase activity after 6 days of cultureas an indicator of bone matrix production by the osteoblasts seeded onthe surface obtained by the method of the invention (03/136/14) withrespect to that of other conventional surfaces.

DETAILED DESCRIPTION OF THE INVENTION

The present invention provides a method for obtaining a surface of atitanium-based metal implant intended to be inserted into bone tissue,hereinafter “method of the invention”, comprising the steps of:

-   -   (a) projecting particles of aluminium oxide under pressure on        the external area of the implant;    -   (b) chemically treating the sandblasted external area of the        implant with an acid composition comprising sulfuric acid and        hydrofluoric acid; and    -   (c) thermally treating the sandblasted and chemically treated        external area of the implant by heating at a temperature of        200-450° C. for 15-120 min.

As indicated above, the surface of a titanium-based implant is thesuperficial layer or outermost area thereof composed mainly by titaniumoxide.

The surface obtained by the method of the invention has a thickness of8-50 nm, particularly of 10-30 nm and more particularly of 15 nm. Saidthickness, which is almost three times the thickness of conventionalsurfaces, involves a greater osseointegration of the implant, inaddition a considerable reduction of the impurities, as has beenpreviously indicated.

Likewise, the surface obtained by the method of the invention comprisesan almost stoichiometric composition of titanium oxide, of approximately98% by weight. (percentage measured by means of XPS, or photoemissionspectroscopy, after 1 minute of sputtering, or bombardment withaccelerated ions, to eliminate the contamination present in the externalarea of the surface obtained, which is inherent to the analysis method,and obtain the actual composition thereof).

The surface obtained by the method of the invention additionally hasgood micrometer-scale roughness and, therefore, very goodosseointegration and cell response properties. In fact, the morphologyof the treated surface is similar to the trabecular bone, optimized forthe start of the bone repair. Likewise, its porosity and roughnesscharacteristics allow the homogenization of residual stresses, theadhesion and fixing of the initial proteins, as well as cell adhesion,proliferation and maturation and the stability of extracellular matrix.

The metal implant to be treated is a titanium or titanium alloy implant.The titanium can be commercially pure titanium, for example. Likewise,the titanium alloy can be any suitable titanium alloy such as thetitanium, aluminium and vanadium alloy Ti6Al4V, for example. Saidtitanium-based metal implant is suitable for being inserted into bonetissue, therefore it can be a dental implant, orthopedic implant, etc.,depending on the bone tissue into which it is intended to be inserted.

In a particular embodiment of said method, the projection of theparticles of aluminium oxide on the external area of the implant of step(a) is performed at a pressure of 1-6 atm. In a preferred embodiment,the projection of the particles of aluminium oxide is performed at apressure of 3 atm.

In another particular embodiment of the method of the invention, theparticles of aluminium oxide used in step (a) have a particle size of10-100 μm. In a preferred embodiment, said particles of aluminium oxidehave a particle size of 25 μm.

Upon sandblasting with particles of aluminium oxide, biocompatibilityproblems are prevented from occurring in the event that there areremains of such particles at the end of the process, since it is a verybiocompatible material. Furthermore, the particles of this material andsize have numerous sharp arrises and edges, which, combined with thepressure of the sandblasting, cause a point of impact with a pronouncedconcave shape, suitable for the good cell response.

Any suitable device, such as Renfert brand Basic Quattro modelsandblasting equipment can be used to perform the sandblasting, orhomogenization of machining stresses. Said equipment is connected to apressurized air circuit, which projects the aluminium oxide grit withwhich the machine is loaded. Once the sandblasting is over, the surfaceis cleaned by any suitable method of the art, such as by applyingpressurized air and subsequent ultrasound cleaning treatment.

In a particular embodiment of the method of the invention, the acidcomposition used in step (b) comprises 15-50% (v/v) sulfuric acid and0.01-1% (v/v) hydrofluoric acid. In a preferred embodiment, said acidcomposition comprises 28.8% (v/v) sulfuric acid and 0.024% (v/v)hydrofluoric acid.

This particular combination of acids produces a particular roughness andmorphology which, combined with the surface chemical compositionobtained with hardly any impurities, cause an optimal cell response.

In another particular embodiment of the method of the invention, thechemical treatment of step (b) is performed at a temperature of 50-110°C. for 4-60 min. In a preferred embodiment, said chemical treatment isperformed at a temperature of 75° C. for 12 min.

Standard laboratory implements are used for the etching, inside a fumehood (Cruma brand 9001-GH model air hood, for example) to prevent acidvapors. After the chemical treatment, the implant is removed from theacid bath, washed to remove the remaining acid and subsequently cleanedby means of ultrasound and dried. For the drying, a suitableconventional drying device can be used, such as a Renfert brand dryingoven.

In another particular embodiment of the method of the invention, thethermal treatment of step (c) is performed at a temperature of 285° C.for 60 minutes.

This thermal treatment at the indicated temperature and for thestipulated time causes a restructuring of the surface titanium oxidelayer, with an increase of the crystallinity and a reduction of theimpurities, which entails an improvement of the cell response.Furthermore, said thermal treatment increases the thickness of thesurface titanium oxide layer. Under normal conditions, titanium exposedto the atmosphere oxidizes and generates a titanium oxide layer with athickness of about 5 nanometers. This oxide layer protects the rest ofthe titanium from oxidizing. It is thus interesting to obtain a titaniumoxide layer with increased thickness, but not so much that the fragilityof said layer can cause the generation of microparticles upon rubbingwith the bone while inserting the implant. The range of thicknessobtained by the method of the invention of 8 to 50 nm is acceptable inthis sense.

Thus, to obtain the mentioned thickness, the thermal treatment must beperformed at a temperature sufficient to accelerate the diffusion ofatmospheric oxygen in the material, and not high enough to cause anoxidation in the titanium that will be visible by a change in thecolour. The working temperature selected therefore varies between 200°C. and 450° C.

Finally, the treatment time is the second parameter which must becontrolled. A very reduced time does now allow the effective diffusionof oxygen. A time that is too long causes excessive increases in thethickness of the layer and cannot be industrialized. A reasonable rangebetween these two extremes would be located between 15 minutes and 24hours, depending on the treatment temperature. The working time selectedtherefore varies between 15 and 120 minutes.

This thermal treatment is performed by conventional means, using alow-temperature Memmert UM-100 model oven, for example.

In another aspect of the invention, a surface obtainable by thepreviously described method is provided. As has been indicated, saidsurface comprises substantially pure titanium oxide and has a thicknessof 8-50 nm, particularly of 10-30 nm and more particularly of 15 nm.

In another aspect of the invention, a titanium-based metal implantintended to be inserted into bone tissue, having the surface obtainableby the previously described method, is provided. In a particularembodiment, said metal implant is a titanium or titanium alloy implant.In another particular embodiment, said metal implant is a dentalimplant.

The following examples illustrate the invention and must not beconsidered as limiting the scope thereof.

Example 1 Obtaining a Titanium Dental Implant with a Surface Obtainableby the Method of the Invention

A Defcon TSA threaded cylindro-conical endosseous implant made ofcommercially pure titanium was subjected to a projection of 25 μmparticles of aluminium oxide under a pressure of 3 atm, placing the exitnozzle perpendicular to the surface to be treated, at a distance ofbetween 2 and 3 cm. After the sandblasting, it was cleaned withpressurized air and subsequently submersed in pure water in ultrasoundfor 10 minutes. It was then dried by means of compressed air.

An aqueous solution was then prepared with the following composition:28.8% by volume of sulfuric acid and 0.024% by volume of hydrofluoricacid. The beaker with the reagent was placed in a thermal bath, settingthe temperature to be reached by the reagent to 75°+/−2° C. Once thedesired temperature of the reagent was reached, the chemical treatmentwas performed by means of immersing the previously sandblasted implantin the reagent solution for 12 minutes (+/−15 seconds). Once saidtreatment ended, the implant was removed from the acid bath and dilutedby means of shaking for about 15 seconds in two pure water bathsconsecutively. It was then submersed in pure water in ultrasound forabout 10 minutes and subsequently dried in an oven.

Finally, the thus treated implant was subjected to a final thermaltreatment at a temperature of 285° C. (+/−20° C.) for 60 minutes in alow-temperature Memmert UM-100 model oven.

Example 2 Characterization of the Surface Obtained in Example 1Morphology

The morphology of the surface obtained in Example 1 was studied by meansof surface micrographs and measurement of the roughness by confocalmicroscopy.

Surface Micrographs

The surface micrographs were carried out in a JEOL JSM 840 scanningelectron microscope, with a scanning beam potential of 15 kV.

FIG. 1 b shows a (150×) micrograph of said surface in which it is seenthat the surface has very characteristic surface roughness, with valuesof roughness R_(a) (average roughness) of about 1 μm, characterized by arounded morphology with sharp outer edges and the presence of ahomogeneously distributed deep porosity, due to the action of the acidetching on the surface.

This level of roughness allows complying with the requirements indicatedby various scientific articles (Buser et al. 1991, Cochran et al. 1994,Martin et al. 1995, Wennerberg et al. 1996, Wennerberg et al. 1997,Buser et al. 1998, Lazzara et al. 2000, Orsini et al. 2000, supra) inrelation to the need of having on the surface of the implant a roughnessallowing a good anchorage of the cells.

Measurement of the Roughness by Confocal Microscopy

The measurement of roughness in 3D was performed with a confocalmicroscope connected to the software PLμ, developed by the OpticsDepartment of the Escuela Técnica Universitaria de Terrassa (UniversitatPolitècnica de Catalunya). The measurements were made according to theDIN 4768 standard, with an 800 μm cut-off Gaussian filter.

FIG. 2 b shows the roughness in three dimensions of the surface obtainedby means of this technique. Likewise, FIG. 3 shows the reconstruction ofthe sector of an outer thread area of the implant and the measurement ofthe corresponding roughness according to a transverse profile of thesurface.

The values of roughness obtained give average values of R_(a) (averageroughness) of 1.0 μm, with a spacing between peaks S_(m) of 12 μm. Thesevalues are close to the values mentioned as desirable in the literaturereferred to in the previous section.

Surface Chemical Composition

The analysis of the surface chemical composition was performed by meansof two different techniques: analysis by energy-dispersive X-rays (EDS),and analysis by photoelectron spectrometry (XPS).

Analysis by Energy-Dispersive X-Rays (EDS)

This technique allows determining the quantitative composition of asurface in a thickness of approximately 1 μm with a high spatialresolution. EDS allows detecting the presence of atoms with an atomicweight comprised between boron and uranium, and quantifying theirpresence in the studied surface.

The EDS measurements were made in the Scientific-Technical Services ofthe Universitat de Barcelona. A Leica Electroscan 360 SEM, with EDSLink-Inca equipment capable of detecting atoms with an atomic weightequal to or greater than that of boron, was used to that end. FIG. 4shows the energy-dispersive X-ray spectrum (EDS) obtained.

The analyses performed by means of EDS have only shown the presence oftitanium and of oxygen in the surface of the titanium sample treated,with an occasional trace of aluminium. The presence of aluminium is dueto the effects of the previous stress homogenization treatment, whichcan leave some particles of aluminium oxide adhered in the surface. Thedifferent analyses show that this behavior occurs in the entire surfaceof the treated implant.

Analysis by Photoemission Spectrometry (XPS)

The XPS analyses were performed by the ESCA and TEM Analysis Unit of theScientific-Technical Services of the Universitat de Barcelona. Theresults (in atomic percentages) are shown in Table 1, together with acomparison with XPS analyses mentioned in the literature of severaldental implants (Wieland et al., “Measurement and evaluation of thechemical composition and topography of titanium implant surfaces”, BoneEngineering, chap. 14 (2000) J. E. Davies eds; Massaro et al.,“Comparative investigation of the surface properties of commercialtitanium dental implants. Part I: chemical composition”. J Mat Sci: Matin Medicine (2002) 13: 536-548).

TABLE 1 Results of the analysis of the surface of the samples performedwith XPS, compared with those of the surface of other commercialimplants. TiO₂ C O Si N Ti Na Cl Layer (%) (%) (%) (%) (%) (%) (%) (nm)Surface¹ 46.0 38.2 — 2.0 13.8 — — 15 Sputtering 5.1 54.0 — 0.4 38.2 — —15 1 minute² Machined 29.8 51.9 — — 12.8 5.0 0.5 5.7 Brånemark³ ITI SLA⁴34.9 51.4 traces 1.3 14.5 — — 5.7 3i Osseotite⁵ 53.7 36.2 3.3 5.4 6.8traces traces N.a. ¹Surface of the invention analyzed without“sputtering” (includes the detection of the contamination present in theoutermost area of the surface obtained and which is inherent to theanalysis method). ²Surface of the invention after 1 minute ofsputtering. ³Machined Brånemark: without treatment, only mechanicalprocess (Nobel Biocare). ⁴ITI SLA: sandblasting + acid treatment(Straumann). ⁵3i Osseotite: acid treatment (Biomet 3i). N.a.: Notavailable.

The comparison of results shows that the chemical composition of thesurface of the samples analyzed is perfectly equivalent to that of otherimplants present on the market, even with a lower presence of carbon orsilicon impurities (Wennerberg et al. 1996, supra; Wieland et al. 2000,supra; and Sittig et al., “Surface characterization of implant materialsc.p. Ti, Ti6Al7Nb and Ti6Al4V with different pretreatments”, J MaterSci: Mater in Medicine (1999), 10:35-46).

The presence of some elements in the surface, such as nitrogen, is dueto the thermal treatment process. The presence of other contaminantscommon in other processes, such as silicon or sodium has not beendetected. The residual % up to 100% is due to the argon detected (notindicated), which is a residue of the XPS measurement process.

Example 3 Cell Response of the Surface of a Titanium Sample Obtained bya Method Similar to that Described in Example 1

A study was conducted by the 063-13 research group (PharmacologyDepartment, School of Medicine and Odontology, Univ. Santiago deCompostela, Spain) for the biological evaluation of titanium samples(commercial pure titanium discs with a diameter of 5 mm) treated bymeans of a method similar to that described in Example 1.

Human osteoblasts were seeded in work samples (8×10³ cells/disc intriplicate) in modified Dulbecco culture medium, with 10% fetal bovineserum and 1% antibiotic solution. Cell bioactivity (indicator of thecytotoxicity of the surface) and alkaline phosphatase production(indicator of bone matrix production by the osteoblasts) of the surfaceobtained by the method of the invention (code 03/136-14) were measuredwith respect to those of an untreated surface of the same titaniummachined (code 03/136-07), another untreated surface of the sametitanium subjected to sandblasting (polished with silicon carbidepolishing paper of about 5 micrometers) (code 03/136-18) and anuntreated surface subjected to sandblasting plus acid treatment similarto the ITI SLA surface (code 03/136-09).

FIG. 5 shows the results of the measurement of cell viability at 12, 24and 72 hours in said samples. FIG. 6 in turn shows the results of themeasurement of alkaline phosphatase activity after 6 days of culture ofsaid samples.

Alkaline phosphatase activity has long been associated to biologicalcalcification. Thus, the improved expression of this enzyme seems to benecessary before the mineralization of the bone matrix, providing thelocalized enrichment of inorganic phosphate for the nucleation andproliferation of hydroxylapatite crystals, the main component of bonetissue.

As can be seen in said FIGS. 5 and 6, the results obtained show a bettercell response by the surface obtained by the method of the invention(code 03/136/14) with respect to the surface of the machining (code03/136/07) and sandblasting (code 03/136/18) controls. On the otherhand, the results of cell response of the surface of the invention areequivalent to those of the sandblasting and acid treatment control (code03/136/09).

1. A titanium-based metal implant surface obtainable by a processcomprising: (a) projecting particles of aluminium oxide under pressureon an external area of the implant to form a sandblasted external area;(b) cleaning the sandblasted external area with pressurized gas, toprovide a cleaned sandblasted external area; (c) chemically treating thecleaned sandblasted external area with an acid composition comprisingsulfuric acid and hydrofluoric acid to form a sandblasted and chemicallytreated external area; and (d) thermally treating the sandblasted andchemically treated external area by heating at a temperature of 200-450°C. for 15-120 minutes to form the treated surface; wherein the acidtreatment step, step (c) results in additional pitting of the cleaned,sandblasted external area.
 2. The surface of claim 1, wherein saidsurface comprises substantially pure titanium oxide.
 3. The surface ofclaim 1, wherein said surface has a thickness within the range of from 8nm to 50 nm.
 4. The surface of claim 3, wherein said surface has athickness of from 10 nm to 30 nm.
 5. The surface of claim 4, whereinsaid surface has a thickness of about 15 nm.
 6. The surface of claim 1,wherein said surface has a micrometric-scale roughness.
 7. The surfaceof claim 1, wherein the pressurized gas is pressurized air.
 8. Thesurface of claim 1, wherein the projection of the particles of aluminiumoxide on the external area of step (a) is performed at a pressure of 1-6atm.
 9. The surface of claim 8, wherein the projection of the particlesof aluminium oxide on the external area of step (a) is performed at apressure of 3 atm.
 10. The surface of claim 1, wherein the particles ofaluminium oxide used in step (a) have a particle size of 10-100 μm. 11.The surface of claim 10, wherein the particles of aluminium oxide usedin step (a) have a particle size of 25 μm.
 12. The surface of claim 1,wherein the acid composition used in step (c) comprises 15-50% (v/v)sulfuric acid and 0.01-1% (v/v) hydrofluoric acid.
 13. The surface ofclaim 12, wherein the acid composition used in step (c) comprises 28.8%(v/v) sulfuric acid and 0.024% (v/v) hydrofluoric acid.
 14. The surfaceof claim 1, wherein the chemical treatment of step (c) is performed at atemperature of 50-110° C. for 4-60 minutes.
 15. The surface of claim 14,wherein the chemical treatment of step (c) is performed at a temperatureof 75° C. for 12 minutes.
 16. The surface of claim 1, wherein thethermal treatment of step (d) is performed at a temperature of 285° C.for 60 minutes.
 17. A titanium-based metal implant comprising a surfaceof claim
 1. 18. The implant of claim 17, wherein said implant issuitable for insertion into bone tissue.
 19. The implant of claim 18,wherein said implant is a dental implant.